Stimulation procedures often require the use of well treating materials having high compressive strength. In hydraulic fracturing, such materials must further be capable of enhancing the production of fluid and natural gas from low permeability formations.
In a typical hydraulic fracturing treatment, fracturing treatment fluid containing a solid proppant material is injected into the wellbore at high pressures. Once natural reservoir pressures are exceeded, the fluid induces fractures in the formation and proppant is deposited in the fracture, where it remains after the treatment is completed. The proppant material serves to hold the fracture open, thereby enhancing the ability of fluids to migrate from the formation to the wellbore through the fracture. Fractured well productivity depends on the ability of a fracture to conduct fluids from a formation to a wellbore. Since fracture conductivity is an important parameter in determining the degree of success of a hydraulic fracturing treatment, selection of a proppant is often critical.
Conventional proppants, such as sand and glass beads and bauxite, as well as resin-coated sands, intermediate strength ceramics and sintered bauxite, are characterized by a fairly high apparent specific gravity (ASG). For instance, the ASG for sand is about 2.65 and the ASG for sintered bauxite is 3.4. Proppant transport is often difficult with such proppants. Further, higher ASG proppants (greater than 2.65) often cause a reduction in propped fracture volume, based on equivalent mass of proppant, which, in turn, causes a reduction in fracture conductivity. The high ASG of such conventional proppants is known to be the controlling factor in the difficulties in proppant transport and reduced propped fracture volume.
More recently, ultra lightweight (ULW) materials have been used as proppants. ULW proppants are typically characterized by an ASG less than or equal to 2.45 and exhibit better deformability than conventional heavy proppants. ULW proppants, in addition to having lower ASG than conventional heavy proppants, typically exhibit sufficient strength to withstand the rigors of high temperatures and high stresses downhole. While offering excellent compressive strength, ULW proppants often soften and loose their compressive strength especially at high temperature and high pressure downhole conditions. Alternatives have therefore been sought.
It is desirable that such alternative materials, when used in a fracturing fluid containing water, salt brine or slickwater be capable of creating a partial monolayer of proppant in the fracture. In conventional sand packs, tightly held packs often are characterized by insufficient interconnected interstitial spaces between abutting particulates. Increased interstitial spaces between the particulates are typically desired in order to increase conductivity. This may be achieved by use of a partial monolayer fracture wherein reduced volume of proppant particulates in a fracture is created by the use of widely spaced proppant particulates. Increased fracture conductivity results since the produced fluids typically flow around the widely-spaced proppant particulates rather than through the interstitial spaces in a packed bed. The phenomena of partial monolayer fracturing has been discussed in the literature. See, for instance, Brannon et al, “Maximizing Fracture Conductivity with Partial Monolayers: Theoretical Curiosity or Highly Productive Reality” SPE 90698, presented at the SPE Annual Technical Conference and Exhibition, Houston, Sep. 26-29, 2004. Unfortunately, partial monolayer fracturing has been difficult to achieve with state-of-the-art proppants.
Improved well treating materials have also been sought for use in the prevention of sand grains and/or other formation fines from migrating into the wellbore. When such migration occurs, such grains and fines typically reduce the rate of hydrocarbon production from the well. In addition, such grains and fines can cause serious damage to well tubulars and to well surface equipment.
Gravel packs are often used to control migration of formation sands and/or fines in producing formations into the production tubing. In a gravel pack installation, gravel is placed between the screen and the formation sand and/or fines. The produced fluids enter the production tubing through the wire screen. The wire screen, typically positioned in an open hole or inside the well casing, has very narrow openings which are large enough to permit the flow of formation fluid but small enough to bridge the formation sands and/or fines from passage through the screen. A gravel pack, which typically consists of uniformly sized spherical particulates, is further packed around the exterior of a screening device. Such spherical particulates operate to trap, and thus prevent the further migration of, formation sand and/or fines which would otherwise be produced along with the formation fluid.
In order to be useful in gravel packing applications, such spherical particulates must exhibit high strength and be capable of functioning in low permeability formations. ULW well treating materials have been proposed for use in gravel packing applications to improve transport, placement, and packing efficiency. Concerns exist however that ULW materials do not demonstrate the chemical resistance properties required of particulates for use in gravel packing.
Alternative well treating materials have therefore been sought which exhibit high compressive strength and which may be used to improve packing efficiency, transport and placement of proppant in fracturing. It is further desired that such materials be useful in other oilfield treatment processes, such as sand control.